Consistency regulator



Oct. 9, 1962 D. E. READ ETAL CONSISTENCY REGULATOR Filed May 25, 1959 INDICATOR CONTROL FIG.3

INVENTORS DOUGLAS E.READ

WILLIAM B. CRANFORD y FREDERICK w. MAJOR RICHARD E. SMITH ATTORNEY 3,tl57,l87 tJUNSISTENCY REGULATOR Douglas E. Read, Wiiliam B. Crantord, and Frederick W. Major, Hawireshury, Ontario, and Richard E. Smith, Gttawa, Gntario, Canada, assignors to Canadian International Paper Company, Montreal, Quebec, Canada, a corporation of Quebec, Canada Filed May 25, 1959, er. No. 815,630 9 Claims. (El. 73-61) This invention relates to a consistency measuring device in a consistency regulator for the measurement and regulation of the consistency of fibre suspensions, for instance, cellulose pulp stock. It pertains particularly to the lower ranges of consistency as used in screening operations and in the highly diluted pulp stock flowing to the Fourdrinier wire on a paper machine.

The control of pulp stock consistency, i.e., proportion in percentage of solid fibre content to water in a pulp stock suspension, is important at the various stages in pulp stock preparation in the pulp mill and in its progress to the wet end of the paper machine and particularly at the latter point where the pulp stock suspension flows onto the horizontal moving Fourdrinier wire screen where the fibres are deposited in the form of a wet mat which forms the paper web as the water flows down through the screen. Variation in consistency are highly undesirable particularly because they cause unevenness in the thickness or weight of the paper being formed.

In the earlier and intermediate stages of pulp preparation, the pulp consistencies may be of the order of 6 to 12%, but in the final stage of stock flow onto the wire, the consistency is much lower, usually of the order of 1% or less.

A consistency regulator is used at various points in stock preparation to maintain consistency at a predetermined level as closely as possible. It senses variations in consistency and in response to the variations it actuates control mechanisms including one or more valves to readjust the proportion of fibre and water flowing past the control point.

The responsive control equipment is pretty well standardized and highly accurate to a satisfactory degree. The measuring equipment which senses the consistency variations in the first instance is what is crucial to the successful operation of a consistency regulator.

A variety of known consistency measuring devices for pulp consistency regulators are satisfactory in the higher consistency ranges. In general they depend upon a number of different principles such as frictional resistance of the interface of the fibre suspension and the walls of a tube, trough or other member, upon the interfacial friction between the stock and a rotating or movable member, upon buoyant force, transmitted light, radio frequency signal resonance, vibrations, pressure changes, and others.

While the known devices work satisfactorily under particular conditions and for particular purposes, especially in the higher ranges of consistency, they are all subject to limitations and inaccuracies of one kind or another, particularly at low consistencies. The previous devices fail at low consistencies for a number of reasons including the well-known fact that in low consistency ranges the interfacial friction may be equal to or even lower than that of water containing no suspended fibers.

It, therefore, remains a problem and, accordingly, a broad objective of the present invention to provide a consistency regulator including a consistency measuring device which is more accurate and dependable, particularly at lower consistencies.

Other objects are to provide means for measurement and control of consistency not disturbed by freeness varia- 3,57,l87 Patented Oct. 9, 1962 2 tions normally encountered in paper manufacture, to avoid the disturbance which is caused by the build-up of solids in most other devices of similar purpose, and to provide a device combining sensitive precision with simplicity, eliminating unnecessary mechanical complications. Further objects will be apparent from the description.

The invention takes advantage of the principle that variation in the internal friction of the fibre suspension is proportional to variation in stock consistency and its usefulness is in large part due to the direct and simple method by which this property may be measured with the novel apparatus according to the invention, without confusion with other properties. The principle is distinctly different from any of the principles upon which previous consistency-measuring methods are based.

If a pulp stock suspension is put in motion, the length of time that it will take in coming to rest will be inversely proportional to the consistency because of the increase of internal friction which increases with consistency. Our invention takes advantage of this property by imparting a constant spinning motion to a flowing stock suspension and measuring the spin remaining at a fixed distance farther along. The residual spin decreases as the consistency increases because of the damping effect of the increase in solids content of the suspension. The sensitivity of the relation of residual spin (rotation) to stock consistency and the ease with which the spin may be converted into signals, electrical and other, suitable for operating measuring, recording, and regulating devices, combine to make this apparatus and method remarkable for simplicity and effectiveness.

The invention is further described in connection with the accompanying drawings in which:

FIG. 1 is a schematic elevation of a typical embodiment of the complete assembly,

FIG. 2 is a section taken on 2--2 of FIG. 1 showing the tangential stock inlet,

FIG. 3 is a partial schematic elevation of a modification showing another arrangement for imparting rotary motion to the stock.

In the drawings, FIG. 1, a constant level headbox 10 has a main stock inlet 12 and outlet '14 by means of which a stream of the stock suspension under measurement is passed constantly through the headbox.

A cylindrical hollow column '16 is arranged below the headbox 10 and connected to it by a bypass stock flow line 1-8 which extends from the bottom of the box 10 at 20 to the bottom of the column 16 at 22.

A baffle 9 in the headbox 10 maintains the stock at a constant level 13 in the headbox 10 above the line 18, and a baffle 11 is provided to reduce turbulence between the discharge end of the line 12 and the intake end of the line '18.

As best seen in FIG. 2, the line 18 enters the column 16 tangentially of the column 16 at the connection 22.

The column 16 may be secured in a vertical position as by brackets 24 attached to a panel 41 or other convenient support structure. Attached at the top of the column \16 is an overflow boX 26, annular in shape and surrounding the top of the column so as to catch the stock which flows upwardly through the column 16 and over its top edge 28. A line 30 attached at the bottom of the overflow box 2 6 is arranged to conduct stock away and to return it to a convenient point in the stock flow system.

A sensing device in the form of a vane 32, conveniently of a two bladed (single vane) design, is rotatably mounted within the top of the column 16 below its upper edge 28 and coaxially with the column 16. The vane 32 is supported on a shaft 34 which extends through a frictionless bearing 36 in a cover 38 on top of the overflow box 26 and whichconnects the vane 32 with signal transmission means comprising a tachometer device conveniently in the form of an electric generator 40 supported on the panel 41. The tachometer 40 is operated by the vane 32 to transmit a voltage signal proportionate to the rate of rotation of the vane 32.

The tachometer-generator 40 is operatively connected as by wires 42 and 43 to an indicator and control device 44 which may be of any convenient known type responsive to voltage variations. The indicator and control device 44 indicates voltage variations and may in turn also actuate control apparatus (not shown) for varying the consistency of the stock which flows into the headbox through the line 12.

In operation, part of the pulp stock suspension is maintained at a constant level 13 in the headbox 10 above the line 18 and is diverted from its main flow over the bafile 11 and out of the main outlet 14, so that it flows also downwardly through the by-pass line 18 into the column 16. The constant pressure head established by the constant stock level 13 imparts a constant flow to the stock in the column 16 and, because of the tangential connection 22 of the line 18 with the column, it imparts to the stock in the column 16, as indicated by the arrow in FIG. 2, a constant rotary motion or spin as well. The stock flows upwardly through the column '16 with the rotary motion.

The residual rotation or spin remaining in the stock in the column 16, just before it flows upwardly over the top edge 28 of the column and into the overflow box 26, is imparted to the sensing device 32 and thence through the shaft 34 to the armature of the tachometer-generator 40. The indicator-control device 44- is responsive to the signal voltage output of the tachometer-generator 40 and shows a decrease in voltage with an increase in stock consistency. It may be calibrated in terms of stock consistency.

The stock flowing from the top of the column 16 is collected in the overflow box 26 and leaves it through the line 30 by which it is returned to the system at a selected point.

Since the rotational speed of the outgoing stock bears an accurate relation to consistency, the resulting rotational speed of the sensing device 32 furnishes an accurate means of measuring stock consistency, and its variations. These variations are used to correct and control consistency in response to the indicator control device 44.

FIG. 3 shows an alternative arrangement for imparting rotary motion to the stock.

The apparatus shown in FIG. 3 includes a column 16a fragmentarily illustrated because the upper part of it is arranged and operates exactly as in FIG. 1. In place of the tangential arrangement of the column 16 and stock input line 18 of FIGS. 1 and 2 a stock input line 18a leads at 19 to the bottom of the column 16a so that the axis of the line 18a and column 16a intersect. The rotary motion is imparted to the stock flowing upwardly from the bottom of 1611 by an impeller 46 mounted on a shaft 48 extending through a gland 50 at the bottom of the column 16a and driven at a preselected constant speed by a pulley 52 and a belt 53 connected to power means (not shown) preferably with provision for varying speed. The impeller 46 may be in the form of a single flat vane providing two blades or of 2 vanes at 90 providing 4 blades.

I The apparatus may be varied in design and operation within the scope of the invention. For instance, it may be desirable to operate with downward flow of the stock, with modifications of design apparent to those skilled in the art. It may in some cases be convenient to replace the constant level headbox by other means such as a metering pump giving the desired constant rate of stock flow into the column.

Dimensions of the apparatus may be varied widely without seriously impairing the accuracy of stock consistency measurements. On account of practical space limitations, flow characteristics of thin stocks and the like, it has been found convenient to use a column 16 or 16a which is three inches in diameter and of such a length that the distance between the stock inlet point 22 or 19 and vane 32 is forty-two inches. The vertical head between the stock level 13 and the stock inlet 22 in the apparatus of FIGS. 1 and 2 has been conveniently found to be fifteen feet.

-It has been found that by varying the height of the pressure head and consequently the flow and the rotational speed of the stock moving from the bottom of the column 16, the sensitive range of the apparatus may be shifted and the sensitive range will vary depending somewhat also on the type of pulp in the suspension, for instance, as between sulphite and groundwood stock. An increase in stock rotational speed generally speaking shifts toward higher consistencies the sensitive range of operation in consistency measurement.

Variations and type of pulp may vary or broaden the accurate range of consistency measurement. For instance, consistency measurements on sulphite pulp provide accurate consistency measurement over a range between 0.35 and 1.3% consistency with a fifteen foot pressure head to stock inlet 22, with a column 16 diameter of three inches and with forty-two inches between stock inlet 22 and bottom of sensing device 32. Measurements under the same conditions with groundwood stock show an accurate range between 0.6 and 1.1% consistency.

The same consideration applies to the use of the impeller 46 of FIG. 3. With a much lower pressure head, in which the distance between the headbox 10 and the top of the column 16a is forty inches, and with the impeller 46 in four bladed form driven at 538 r.p.m., good sensitivity of consistency measurement is found between 0. 1 and 0.6% consistency. Increasing the impeller speed to 700 rpm. provides a sensitive consistency measure of \between 0. 1 and 0.8%. Further increasing the impeller speed to 1180 rpm. reflects a higher pick-up speed of the sensing device 32 and of the voltage from tachometergenerator 40 with a sensitive consistency measurement range between 0.3 and beyond 0.8%.

Apparatus of FIGS. 1 and 2 arranged to regulate consistency of stock shows a maximum consistency variation of :0.0l8% when samples of the regulated stock are taken at one minute intervals over a fifteen minute period.

It is apparent that other methods for converting the speed of rotation of the stock leaving the column of the apparatus to measurable signals may be adapted within the scope of the invention.

It is further apparent that the apparatus of the invention is particularly useful in accurate consistency measurements or consistency control involving pulp stock consistencies below 1 We claim:

.1. Apparatus for measuring the consistency of fibrous stock as a suspension comprising a cylindrical hollow column having an inlet and an outlet spaced from said inlet axially of said column, means to maintain a constant pressure head in said inlet to cause said stock to flow through said column between the inlet and the outlet, said inlet being connected tangentially to said column thereby to impart a constant rotary motion to said stock as it starts to flow through said column, a rotatable vane mounted coaxially in said column near said outlet responsive to the residual rotary motion of said stock as it approaches said outlet, a tachometer-generator operated by said vane, and indicating and control means responsive to said tachometer-generator.

2. Apparatus for measuring the consistency of fibrous stock as a suspension comprising a cylindrical hollow column having an inlet and an outlet spaced from said inlet axially of said column, means to supply a constant flow of stock through said inlet to said column, means including a rotatable impeller mounted coaxially in said column near said inlet to impart a constant rotary motion to said stock as it starts to flow through said column, means to rotate said impeller, a rotatable vane mounted coaxially in said column near said outlet responsive to the residual rotary motion of said stock as it approaches said outlet, a tachometer-generator operated by said vane, and indicating and control means responsive to said tachometer-generator.

3. Apparatus for measuring the consistency of fibrous stock as a liquid suspension comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, a first means to cause said stock to flow at constant rate through said column between the inlet and the outlet, a second means to impart a constant rotary motion to said stock as it starts to flow from said inlet and through said column, and rotation measuring means in said column near said outlet, said rotation measuring means being operable variably and independently of the first and second means and in response to the residual rotary motion of said stock as it approaches said outlet.

4. Apparatus for measuring the consistency of fibrous stock as a liquid suspension comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, a first means to cause said stock to flow at constant rate through said column between the inlet and the outlet, a second means effective at said inlet to impart a constant rotary motion to said stock as it starts to flow from said inlet and through said column, and rotating rotation measuring means in said column near said outlet, said rotating means being operable variably and independently of the first and second means and in response to the residual rotary motion of said stock as it approaches said outlet.

5. Apparatus for measuring the consistency of fibrous stock as a suspension comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, a first means to maintain a constant pressure head in said inlet to cause said stock to flow at a constant rate through said column between the inlet and the outlet, a second means eifective at said inlet to impart a constant rotary motion to said stock as it starts to fiow through said column, and rotation measuring means in said column near said outlet, said rotation measuring means being operable variably and independently of the first and second means and in response to the residual rotary motion of said stock as it approaches said outlet.

6. Apparatus for measuring the consistency of fibrous stock as a suspension comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, means to supply a constant fiow of stock through said inlet, said inlet being connected tangentially to said column thereby to cause said stock to flow through said column between the inlet and the outlet and to impart a constant rotary motion to said stock as it starts to flow through said column, and rotation measuring means in said column near said outlet, said rotation measuring means being operable variably and independently of the constant flow supply means and in response to the residual rotary motion of said stock as it approaches said outlet.

7. Apparatus for measuring the consistency of fibrous stock as a suspension introduced into the apparatus at a constant flow comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, means to impart a constant rotary motion to stock which is caused to flow at a constant rate from said inlet and through said column, a rotatable vane mounted coaxially in said column near said outlet, said vane being operable variably and independently of said constant rotary motion means and in response to the residual rotary motion of said stock as it approaches said outlet, signal transmission means operated by said vane to transmit a signal proportionate to the rate of rotation of said vane, and indicator means operable in response to said transmission means.

8. Apparatus for measuring the consistency of fibrous stock as a suspension introduced into the apparatus at a constant flow comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, means including a rotatable impeller mounted coaxially in said column near said inlet and operable to impart a constant rotary motion to stock which is caused to flow at a. constant rate from said inlet and through said column, means to rotate said impeller, and rotation measuring means in said column near said outlet, said rotation measuring means being operable variably and independently of said impeller and in response to the residual rotary motion of said stock as it approaches said outlet.

9. Apparatus for measuring the consistency of fibrous stock as a liquid suspension introduced into the apparatus at a constant flow comprising a cylindrical hollow column having an inlet and an outlet, said inlet and outlet being spaced from each other axially of said column, means to impart a constant rotary motion to stock which is caused to flow at a constant rate from said inlet and through said column, and rotation measuring means in said column near said outlet, said rotation measuring means being operable variably and independently of the constant rotary motion means and in response to the residual rotary motion of said stock as it approaches said outlet.

References Cited in the tile of this patent UNITED STATES PATENTS 913,420 Muntzing Feb. 23, 1909 2,106,574 Moore Jan. 25, 1936 2,382,979 Demb June 24, 1944 2,992,651 Krofta July 18, 1961 

